Orthopedic fixation devices such as plates are frequently coupled to bone with fasteners inserted through holes in the device. For fractures of the long bones such as the humerus or the femur, fractures may be treated by inserting an elongated member into a channel reamed in the intramedullary canal. This elongated member, or “intramedullary nail” as it is known in the art, may provide stability to the bone until the fractured bone segments heal together. Intramedullary nails may be fastened to the bone in which they reside using screws inserted through pre-formed holes in the nail. Corresponding holes may be drilled in the adjacent bone to allow easier insertion of the screws in the bone. These holes can be formed with the aid of a drill guide aligned with the targeted screw hole. A drill may be introduced through the drill guide is thus guided through the screw hole to drill a hole in the bone underlying the screw hole.
In an effort to reduce the total number and length of incisions created when installing the intramedullary nail and inserting the securing fasteners, the drilling and screw insertion process can be performed percutaneously. Thus, an incision may be made in the skin overlying the bone, and a trocar may be inserted into the incision and used to separate the soft tissue to create an initial passage down to the bone. A drill may be inserted through the drill sleeve and used to form a hole in the bone as previously described. A screw insertion sleeve may thereafter be inserted through the passage and used to facilitate engagement of the screw with the screw hole and bone. Advantageously, these three pieces (trocar, drill sleeve, screw insertion sleeve) may be provided as a single unit to facilitate handling and use by the surgeon. Thus, the three pieces may be nested within each other and inserted as a single unit.
To further facilitate use of these three-piece units, at least two of the pieces may be provided with features aimed at preventing separation of the individual pieces while they are being handled by the user. For example, snap rings, ball detents, or threads may be used to secure the pieces together. To remove one piece from the other (e.g. to remove the drill sleeve from the screw-insertion sleeve), the user may pull the pieces apart (in the case of a snap-ring or ball-detent) or may unthread the pieces (where threaded pieces are provided).
Snap-ring locking devices may be difficult to sterilize, and threaded pieces may be difficult to handle in the surgical environment. Thus there exists a need for a multiple piece drill sleeve system having a simple, easy to sterilize design for provisionally retaining at least two pieces of the system with respect to each other, and which allows easy separation of those pieces when desired by the user.